Lily: Just spill it.
Robin: The other week, Barney made a move, but I turned him down. I felt awful for closing the door in his face, but he realized I was right.
[flashback:]
Barney: I'm done trying to get you. I can't do it anymore.
[present:]
Lily: And now I get it.
Robin: Get what?
Lily: You may have closed the door on Barney, but he locked it.
Robin: What? No, he didn't.
Lily: Yeah, he got the last word, and now you want what you can't have, like you always do. It's the classic lobster situation.
[flashback to Robin in a doctor's office:]
Doctor: I'm afraid you're allergic to lobster. You can never, ever, ever have it.
[later, Robin's face is red and horrifically inflamed as she eats lobster:]
Robin: Oh, this... is... delicious.